Indirect ophthalmoscopy lens system and adapter lenses

ABSTRACT

The invention is directed to an ophthalmoscopic or gonioscopic lens system as well as an adapter lens systems for use with such an associated lens apparatus. The indirect ophthalmoscopy lens of the invention for use in examination or laser treatment of a patient&#39;s eye comprises a hand-held, pre-set or fixed system having at least two lens elements, each having first and second surfaces. At least one of the lens elements includes an aspheric surface of revolution. The at least two lens elements are positioned adjacent one another in a housing, such that the refractive properties of each are combined to converge light from an illumination light source to the entrance pupil of the patient&#39;s eye to illuminate the fundus thereof and form a fundus image to be viewed. The adapter lens systems of this invention are designed for use with an associated ophthalmoscopic lens, enabling selective modification of the optical characteristics of the ophthalmoscopic lens system in a predetermined manner. Within the scope of this invention, a plurality of attachments make possible change in the net power, optical imaging characteristics, magnification, laser transmission properties or other characteristics of a particular ophthalmoscopic lens.

TECHNICAL FIELD

The invention relates generally to lens systems and adapter lens systemsfor use in ophthalmic examination or treatment procedures. Moreparticularly, the invention relates to improved direct and indirectophthalmoscopy lens systems and associated adapter lenses designed foruse with standard ophthalmic instruments providing specific and desiredmagnification and imaging characteristics for improved examination ortreatment of the eye.

BACKGROUND OF THE INVENTION

Indirect ophthalmoscopy techniques are used in diagnostic, therapeuticand surgical procedures in the field of ophthalmology, and normallyinclude the use of positive power lens systems in conjunction with anobserving optical system such as a indirect ophthalmoscope, slit lampbiomicroscope, or operating microscope. Lenses conventionally used inindirect ophthalmoscopy applications often perform the dual functions ofcondensing light from a light source toward the pupil of the eye toilluminate the fundus, and forming an inverted real aerial image of thefundus which can be viewed with either a monocular or binocular device.Indirect ophthalmoscopy systems have been found to be superior to otherexamination or treatment methods, in particular in the examination of aretinopathies, retinal separation, retinal tumors, intraocular foreignbodies, and provide the ability to see fundus lesions which otherwisemay not be observable when opacities of the ocular media are present.Hand-held lenses used in indirect ophthalmoscopy have been of a varietyof types, each affording various advantages in the examination of thefundus. In the development of indirect ophthalmoscopy, hand-held lensesoriginally comprised a single lens element having plane and/or convexspherical surfaces and were of low power. The aerial image produced withsuch a lens was magnified and inverted, and considerably blurred,particularly toward the periphery of the formed aerial image. Atwo-element Ramsden style indirect ophthalmoscopy lens was thereafterproduced by Rodenstock utilizing a spherical convex surface on each ofthe lens elements. This lens provided improved optical quality over thatof a single lens using spherical surfaces, but resulted in increasedsurface reflections and light loss which outweighed the limited benefitsof the insufficiently improved image quality. There has also beenreported the use of a "periscopic lens" for use in slit lamp funduscopy.The periscopic lens included a double plano-convex lens system similarto the Ramsden style indirect ophthalmoscopy lens, but of smallerdiameter and higher power. The periscopic lens system also utilizedspherical surfaces, such that only limited improvement in opticalquality was realized and a reduced field of view was obtained.

Subsequently, improvements were noted by the use of slightly higherpowered single element lenses, each having one aspheric surface with theother surface being plano or spherical. Although the use of a singleaspherical surface in the indirect ophthalmoscopy lens did show greatimprovement over spherical indirect ophthalmoscopy lenses, lensaberrations remained. Thus, the formed aerial image of the fundus stillhad aberrations and increasing astigmatic effects particularly in theperipheral regions of the image.

These designs were subsequently improved upon by the use of twoaspherical surfaces incorporated into the indirect ophthalmoscopy lens.The first use of a double aspheric indirect ophthalmoscopy lens designedfor use with an indirect ophthalmoscope was described in U.S. Pat. No.4,738,521 by David Volk. This lens design incorporates both front andback aspheric surfaces of revolution of conoid type, which substantiallyimproved the quality of the formed aerial image by reducing aberrationsincluding field curvature, astigmatism and distortion. The use of doubleaspheric lenses has been found to be a distinct advantage in indirectophthalmoscopy and has made possible the use of much stronger lenseswhile providing increased clarity of the image as well as increasedfield of view. More recently, a symmetrical double aspherical indirectophthalmoscopy lens particularly suited for use with a slit lampbiomicroscope was developed by David Volk, and described in U.S. Pat.No. 4,627,694. The double aspheric lenses shown in this patent were ofsmaller diameter and higher power, with the aspheric surfaces describedas providing improved correction of aberrations, including fieldcurvature, astigmatism, and distortion. Lenses made according to thisdesign have demonstrated themselves to be better suited for use with theslit lamp biomicroscope, and have yielded significant improvement in theexaminer's ability to see details in the aerial image of the fundus. Thesingle element double aspheric lens thus provided improved imaging aswell as wide field viewing of the fundus, particularly for use with aslit lamp biomicroscope.

In the development of indirect ophthalmoscopy lens systems, it is seenthat particular lenses are best for use with a slit lamp or otherbiomicroscope, while other lens systems are more suited for use with anindirect ophthalmoscope or other observation system. For example, thelonger focal length, lower power indirect ophthalmoscopy lens systemsare not suitable for use with a slit lamp biomicroscope, as theobservation of the formed aerial image would require positioning of thebiomicroscope at a location which exceeds the range of travel built intothe instrument. The development of the double aspheric indirectophthalmoscopy lens as described above has enabled use of higher powerlenses to provide a shorter working distance within the range ofadjustment of the slit lamp biomicroscope to facilitate its use as theobservation optical system, instead of an indirect ophthalmoscope or thelike. It thus may be seen that a particular diagnostic or therapeuticprocedure may require the use of a lens system which is particularlydesigned for that procedure only, thus requiring the practitioner topurchase and maintain a variety of lens systems on hand to achieve thebest results for other particular procedures. Based upon the foregoing,it is clearly desirable to provide the practitioner an indirectophthalmoscopy lens system which may be modified in a specific andpre-determined manner such that a variety of examination or treatmentprocedures are possible.

Similar in this respect to indirect ophthalmoscopy lens systems, otherophthalmic lens systems have inherent limitations as it relates toexamination or treatment procedures. For example, direct ophthalmoscopicobservation techniques utilize a direct ophthalmoscopy lens system whichproduce a virtual image of the eye fundus having particularmagnification characteristics. With both such direct and indirectophthalmoscopic lens systems, there exists no ability to modify theinherent magnification, field, or imaging characteristics of the system,thereby limiting their use. Similarly, gonioscopic lenses forexamination and treatment of the anterior chamber angle of the eye arealso limited in optical performance, having specific magnification andfield characteristics. In these various lens systems for examination andtreatment of the eye, no provision exists for the modification ofinherent imaging characteristics of the lens itself and thus theresulting field characteristics and magnification of the producedvirtual or aerial image. Only with the slit lamp biomicroscope oroperating microscope does there exist the ability to changemagnification, not of the viewed image itself, but as a secondaryadjustment of the Keplerian telescope observation system.

SUMMARY OF THE INVENTION

Based upon the foregoing, it is a main object of the present inventionto provide an ophthalmoscopic lens system which enables its imagingand/or magnification characteristics to be modified in a predeterminedmanner to facilitate its use in a particular diagnostic or treatmentprocedure.

Another object of the invention is to provide an indirect ophthalmoscopylens system which utilizes at least two lens elements cooperating withone another to enhance light condensing functions of the lens system forillumination of the eye fundus, as well as imaging characteristics ofthe lens.

A further object of the invention is to provide adapter lens systems foruse with an associated ophthalmoscopic or gonioscopic lens system toallow the characteristics of the ophthalmoscopic or gonioscopic lenssystem to be modified in a predetermined manner.

The invention is therefore directed to an ophthalmoscopic or gonioscopiclens system as well as an adapter lens systems for use with such anassociated lens apparatus. The indirect ophthalmoscopy lens of theinvention for use in examination or laser treatment of a patient's eyecomprises a hand-held, pre-set or fixed system having at least two lenselements, each having first and second surfaces. At least one of thelens elements includes an aspheric surface of revolution with itsmagnitude and shape defined by the polynomial expressed as follows:

    y=(2rx+(e.sup.2 -1)x.sup.2).sup.1/2 +Ax.sup.F +Bx.sup.G +Cx.sup.H ;

where r equals the apical radius of curvature of each surface, e equalsthe apical eccentricity of each surface, and co-efficients A, B, and C,when used, represent successive terms in the polynomial, and F, G, and Hequal exponents in the successive terms. The at least one asphericsurface of the lens system is chosen to correct astigmatic imagery ofthe lens, such that the lens system forms an aerial image substantiallyfree of excessive field curvature and astigmatism. The indirectophthalmoscopy lens system may be adapted to be hand held, with the atleast two lens elements being positioned adjacent one another in ahousing, such that the refractive properties of each are combined toconverge light from an illumination light source to the entrance pupilof the patient's eye to illuminate the fundus thereof. The at least twolens elements are held relative to the patient's eye at a distancecorresponding to the secondary focal distance of the lens elements withtheir refractive properties combined.

The adapter lens systems of this invention are designed for use with anassociated ophthalmoscopic lens, enabling selective modification of theoptical characteristics of the ophthalmoscopic lens system in apredetermined manner. Within the scope of this invention, a plurality ofattachments make possible change in the net power, optical imagingcharacteristics, magnification, laser transmission properties or othercharacteristics of a particular ophthalmoscopic lens. The adapter lenssystem comprises at least one adapter lens element including first andsecond surfaces positioned within an adapter housing. The adapterhousing includes means for selective attachment to the housingassociated with an ophthalmoscopic lens system, wherein upon attachmentof the adapter housing to the housing of the ophthalmoscopic lens, theat least one adapter lens element is positioned in predeterminedrelationship to a lens of the ophthalmoscopic lens device so as tomodify the optical characteristics of the ophthalmoscopic lens system ina selective and predetermined manner.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention will be obtained upon a furtherreading of the detailed description in conjunction with the drawingswherein:

FIG. 1 is a schematic illustration of an indirect ophthalmoscopy lenssystem in accordance with the invention;

FIG. 2 shows a first embodiment of an adapter lens system in accordancewith the invention;

FIG. 2a shows the adapter lens system of FIG. 2 in use with an indirectophthalmoscopy lens system:

FIG. 3 shows an alternate embodiment of an adapter lens in use with anindirect ophthalmoscopy lens system;

FIG. 4 shows a further embodiment of an adapter lens in use with anindirect ophthalmoscopy lens system;

FIG. 5 shows an adapter lens system for use in association with acontact indirect ophthalmoscopy lens system;

FIG. 6 shows an adapter lens system for use in association with athree-mirror ophthalmoscopic and gonioscopic lens used for performingvarious diagnostic or treatment procedures;

FIG. 6a shows an alternative embodiment of the adapter lens system asshown in FIG. 6;

FIG. 7 shows a set of adapter lenses in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

An indirect ophthalmoscopic lens system in accordance with a firstaspect of the invention is shown in FIG. 1, wherein the lens system 10includes at least two lens elements, with a first lens 12 positionedrelative to a second lens 14 in a housing 15. The lenses 12 and 14condense light from an illumination light source into a patient's eye 16through pupil 18 and onto fundus 20 thereof. In order to obtain thewidest illumination of the fundus 20, the lens system 10 is positionedat a distance from the patient's eye 16, and particularly the pupil 18thereof, such that the back focus of the combined lenses 12 and 14substantially coincides with the pupil 18. The lens system 10 alsogathers light rays emerging from points on the fundus 20 at an imageplane 22. The fundus image is a sharp, clear, aberration-free aerialimage which can be viewed using an indirect ophthalmoscope or slit lampbiomicroscope for example. The fundus image is formed as an aerial imageposterior to the indirect ophthalmoscopy lens system 10. Assuming thatthe eye 16 is an emmetropic eye, each bundle of light rays emerging fromthe eye will be a substantially parallel bundle, with its chief raypassing through the center of the pupil 18. These light rays will beincident upon the indirect ophthalmoscopy lens system 10, initiallyrefracted by the first surface 24 and second surface 26 of lens 12. Thelight rays are thereafter incident upon lens 14, and further refractedby lens surfaces 28 and 30 and focused at the image plane 22. Thebundles of light rays converged by indirect ophthalmoscopy lens system10 will be focused to single points on the image plane 22, with pointson the fundus 20 of eye 16 being represented in the formed aerial image.

The lenses 12 and 14 may be made of a homogenous transparent opticalmaterial, such as ophthalmic grade glass or plastic. In a preferredembodiment, both lens 12 and lens 14 are made of high-grade opticalglass having an index of retraction between 1.4 and 1.9, and preferablywith an index of refraction of 1.883 as an example, for at least one ofthe lens elements. Manufacture of the lens 12 is simplified by utilizingspherical surfaces 24 and 26. In the preferred embodiment, the sphericalsurfaces 24 and 26 are related in a ratio of approximately 1:3, with thesteeper curve of surface 26 facing second lens 14. Similarly, a steepercurve is provided on surface 28 of lens 14 facing lens 12. In thepreferred embodiment, surface 28 will be an aspherical surface ofrevolution, having its magnitude and shape described by the polynomialexpressed as follows:

    y=(2rx+(e.sup.2 -1)x.sup.2).sup.1/2 +Ax.sup.F +Bx.sup.G +Cx.sup.H ;

where r equals the apical radius of curvature of the surface, e equalsapical eccentricity of the surface, and the co-efficients A, B, and C,when used, equal successive terms in the polynomial, with F, G, and Hequaling exponents in the successive terms. The aspherical surface 28will be relatively steeply curved in relation to surface 30 of lens 14,such that the more highly curved surfaces of each of the lens 12 and 14face one another. It has been found that by facing the more steeplycurved surfaces of the lenses toward one another, spherical aberrationinduced from the spherical surfaces in the lens system can be minimizedto a great degree. Additionally, the aspherical surface 28 providesrequired additional correction of spherical aberration as well asprimary field correction to produce a sharp, clear fundus image. In apreferred embodiment, surface 30 of the lens 14 is formed as a sphericalsurface, again being more easily and cost effectively produced ascompared to an aspherical surface on such a lens. Planar surfaces mayalso be used if desired. The provision of at least one asphericalsurface of revolution in the indirect ophthalmoscopy lens system 10allows for correction of primary field aberrations in association withthe self-correcting relationship of the lenses 12 and 14, while allowingcost-effective production of the lens system using additional sphericalsurfaces. In the indirect ophthalmoscopy lens system, the nominal powersof each of the lens 12 and 14 are chosen to yield a nominal power forthe indirect ophthalmoscopy lens system 10 of a desired magnitude.Generally, the indirect ophthalmoscopy lens system 10 of the inventionmay be designed having a nominal power in range between 10 to 150diopters, with lower power lens systems being useful in indirectophthalmoscopy techniques where high magnification of the fundus imageis desired. Higher magnification allows much more detail of the funduspathology to be viewed for examination or treatment.

Alternatively, high power lens systems 10, which are particularly usefulwith the slit lamp biomicroscope, may be used to provide a wide fieldview of the fundus. The use of at least two lenses allows significantlatitude in the particular design criteria for each of the lenses 12 and14, while optimizing the light condensing and imaging-forming qualitiesof the lens system.

It is also a feature of the invention to provide a system by which anophthalmic lens system can be modified for various diagnostic ortreatment uses in a simple and effective manner. For example, given anindirect ophthalmoscopy lens having a nominal power to achievepredetermined magnification, field size and imaging characteristics, thepresent invention enables adaptation of an additional lens or lenses, ofeither positive or negative power, to the ophthalmoscopy lens, thusproviding altered magnification, field size and/or field imagingcharacteristics for various examination or treatment requirements.

In FIG. 2, a first example of an adapter lens system is shown for usewith a commercially available indirect ophthalmoscopy lens. As anexample, an indirect ophthalmoscopy lens 40 may be the commerciallyavailable Volk Double Aspheric 20D lens produced by Volk Optical, Inc.Such a lens is described in U.S. Pat. No. 4,738,521 issued to DavidVolk. In general, a 20 diopter lens of this type will form an aerialimage of the fundus of the eye viewed monocularly using a monocularindirect ophthalmoscope, or binocularly and stereoscopically with abinocular indirect ophthalmoscope at approximately 3X magnification.Although the 20 diopter indirect ophthalmoscopy lens 40 providesmagnification characteristics which are best suited for observing finedetails of the fundus, if additional examination or treatment proceduresare desired to be performed, another indirect ophthalmoscopy lens of adifferent power may be more suited to the task. In accordance with thisinvention, modification of the indirect ophthalmoscopy lens 40 may bemade to allow other beneficial uses in examination or treatment of thepatient's eye. Referring to FIG. 2, lens 40 is positioned within aconventional retainer housing 42, and may be fixed in position by meansof a lens retaining ring 44 screwed into place after insertion of lens40 into housing 42. The adapter lens system of the invention comprisesone or more additional lenses 46 mounted in an adapter housing 48. Theadapter housing 48 may be selectively attached to the housing 42 of theindirect ophthalmoscopy lens 40 on either side of the lens 40 for use inconjunction therewith. For attachment to the indirect ophthalmoscopylens housing 42, the adapter lens housing 48 may include an engageableflexible section 50 having an outer diameter slightly larger than theinner diameter of the housing 42. Alternatively, a compressible andresilient o-ring 52 may be used to frictionally engage the inner surfaceof housing 42, or other suitable means such as resilient fingers may beused to frictionally engage housing 42. Screw threads or any othersuitable means may also be used for selective attachment of the adapterlens housing 48 to the indirect ophthalmoscopy lens housing 42. The useof an o-ring 52 allows an air and watertight seal to be formed,protecting the interior lens surfaces from water or contamination. Theo-ring 52 may be integrally formed in the adapter housing section 50 ormay be provided as a separate member set in a groove machined around thecircumference of area 50 as desired. The resilient engaging means of theadapter lens housing 48 allows selective engagement with a wide varietyof commercial indirect ophthalmoscopy lens housings as desired. Theadapter lens housing 48 may be easily grasped around an external knurledcircumference for example, for engagement with or disengagement fromindirect ophthalmoscopy lens housing 42.

Referring again to FIG. 2, adapter lens 46 comprises a first surface 54and a second surface 56. The surfaces 54 and 56 are preferably sphericalsurfaces which are easily and cost effectively manufactured. In adesired configuration, the spherical surface 56 will have a radius ofcurvature in a ratio of approximately 3:1 to the curvature of surface54, such that the more steeply curved surface 56 is positioned adjacentto indirect ophthalmoscopy lens 40. The adapter lens 46 may have anominal power of 20 diopters, such that in association with the 20diopter indirect ophthalmoscopy lens 40, a high net power combinationsystem is created. With particular diagnostic and treatment applicationsin mind, a set of adapter lenses of varying powers may be provided.

As an example, a set of adapter lenses for use with 20 diopter doubleaspheric indirect ophthalmoscopy lens 40, such as shown in FIG. 2, mayinclude lenses of approximately +4 diopters, +7 diopters, and +20diopters (as shown in FIG. 2), for increasing the power of indirectophthalmoscopy lens system 40. The adapter set may also include minuspowered lenses. As an example, a lens of approximately -4 diopters maybe utilized to reduce power and increase magnification. The adapterlenses may be cost effectively produced from a plastic material usingaspheric surfaces, but other materials or surface configurations such asplanar or spherical may also be used if desired.

According to the example above, FIG. 2a shows a preferred embodiment ofthe "+4D" adapter lens incorporates a symmetrical biconvex lens designwith both radii 54 and 56 equal to 258 mm, a glass index is 1.519, adiameter of 50 mm, and a center thickness of 3.73 mm. The preferred"+7D" lens design may also be biconvex with both radii 54 and 56 equalto 155 mm, a glass index of 1.519, diameter of 50 mm, and centerthickness of 5.28 mm. A preferred "-4D" lens design is meniscus inshape, having a concave radius 54 of 83 mm, a convex radius 56 of 235mm, glass index is 1.519, diameter of 50 mm and center thickness of 1.25mm. The convex surface may be positioned adjacent to the more highlycurved surface of the 20D lens, with the concave surface facing thepractitioner.

In FIG. 3, a further embodiment of an adapter lens system is shown,designed for use with a commercially available 40 diopter indirectophthalmoscopy lens, such as a double aspheric lens, 60, produced byVolk Optical, Inc.. Similar to the previous example of FIG. 2, anadapter lens system comprising adapter lens 62 may be used inassociation with the indirect ophthalmoscopy lens 60 to selectivelymodify the magnification, field of view or imaging characteristics ofthe indirect ophthalmoscopy lens 60. In practice, the 40 diopter doubleaspheric indirect ophthalmoscopy lens 60 has a working distance as wellas magnification and field size characteristics that make it useful withan indirect ophthalmoscope. The indirect ophthalmoscopy lens 60 isgenerally not suitable for use with a slit lamp biomicroscope, as theaerial fundus image is formed at a distance from the patient's eye whichdoes not allow its observation, due to the limitations of thebiomicroscope itself. Generally, the observation system of the slit lampbiomicroscope is movable between extreme positions to adjust to theposition of the fundus image, but such adjustment is limited. Alone, theuse of the 40 diopter indirect ophthalmoscopy lens would requirepositioning of the biomicroscope outside the range of its travel. The 40diopter indirect ophthalmoscopy lens 60 may be combined with an adapterlens 62 also having a nominal power of 40 diopters. The resultingincreased system power of combined lenses 60 and 62 provides an aerialfundus image viewable within the travel allowed by the slit lampbiomicroscope observation system. The addition of the adapter lens 62 tothe optical system also significantly increases the field of view toallow the peripheral retina in the region of the equator and beyond tobe viewed. The resulting lens system including adapter lens 62 may alsobe advantageously used for laser treatment of the eye fundus. In theembodiment of FIG. 3, other adapter lenses may be provided for use withindirect ophthalmoscopy lens 60 to achieve other characteristics ifdesired. The adapter lens 62 may also have spherical surfaces with themore steeply curved surface facing the indirect ophthalmoscopy lens 60in the preferred embodiment. Alternatively, planar or asphericalsurfaces may be used in the adapter lens system if desired.

In a further embodiment of an adapter lens system according the presentinvention, the adapter lens may be a contact lens or lens system used inconjunction with an indirect ophthalmoscopy lens to produce desiredmagnification, field of view, and imaging characteristics. Referring toFIG. 4, contact adapter lens 70 may be used in association with ahand-held indirect ophthalmoscopy lens 85, which in this example is acommercially available double aspheric lens produced by Volk Optical,Inc. Lens 85 represents a high powered lens designed for use with a slitlamp biomicroscope, having a nominal power, for example, in the range of60 to 130 diopters, as described in U.S. Pat. No. 4,627,694, issued toDavid Volk. Lens 85, when used by itself produces a high resolution,wide field image of the fundus. The contact adapter lens 70 can bedesigned to selectively vary the power of the resulting indirectophthalmoscopy lens 85, while providing the various mechanicaladvantages of using a contact lens device. The use of the contact lens76 may facilitate proper positioning of the lens system components inrelation to a patient's eye, and particularly the patient's pupil suchthat the conjugate focus of the slit lamp light source will be locatedat or near the center of the patient's pupil for wide field illuminationof the fundus. The contact lens 76 may be of either positive or negativepower, changing the focal length of the combined optical system andtherefore the system's net power, with a variety of contact adapter lenspowers enabling the desired net power and magnification of thecombination lens system to be achieved.

Referring to FIG. 4, a preferred positive power contact design ofcontact lens 76 includes a corneal contacting surface 76 and an anteriorsurface 78, both of which may be spherical or aspherical in surfaceconfiguration. In the preferred embodiment, the corneal surface 76 hasan apical radius of 7.65 mm and an eccentricity of 0.425, closelymatching the aspherical corneal surface. Anterior surface 78 may have anapical radius of 6.29 mm and an eccentricity of 0.6, correcting for thespherical aberration of the high power contact lens. Center thickness ofthe contact lens may be selected as desired with a preferred thicknessof 3 mm. Alternatively, the contact lens may be a negative power lens,with a preferred negative power contact design including a cornealcontacting surface 76 and an anterior surface 78, again, both of whichmay be spherical or aspherical in surface configuration. In thepreferred embodiment, the corneal surface 76 has an apical radius of7.65 mm and an eccentricity of 0.425. Anterior surface may have anapical radius of 12.93 and be modelled as an oblate spheroid orellipsoid with a (negative) eccentricity value of 0.7. Again, centerthickness of the contact lens may be selected as desired, with apreferred center thickness of 1.35 mm. Also in FIG. 4, there is shownthe possible use of a minus powered adapter lens 86 which is positionedon the anterior side of the indirect ophthalmoscopy lens 85. The minuspowered lens 86 may also be supported within an adapter housing 88 whichprovides selective attachment of the adapter lens system to the indirectophthalmoscopy lens housing. The minus power adapter lens 86 may includeplanar and/or spherical or aspherical surfaces as desired. The additionof a minus power lens 86 to the optical system will produce increasedmagnification and may be used either alone or in combination with acontact adapter lens or other adapter lens system positioned on theposterior side of the indirect ophthalmoscopy lens 85. Similarly, theminus powered lens 86 may be independently positioned on either side ofthe indirect ophthalmoscopy lens depending upon the particularcharacteristics desired.

It is also an aspect of the invention to provide an adapter lens housingwhich allows manual adjustment of the position of the adapter lensoptical system relative to the indirect ophthalmoscopy lens system withwhich it is used. As an example, the adapter lens housing 88 for theminus powered lens 86 is selectively repositionable as shown in ghost toprovide adjustment of the distance between the lenses 85 and 86. Theadjustable positioning of lens 86 allows variable system power to beachieved using the same adapter lens. It should be recognized that uponpositioning of the minus powered lens 86 in close proximity to indirectophthalmoscopy lens 85, the system power will be reduced to the maximumdegree. Upon moving lens 86 away from lens 85 as shown in ghost, the netpower of the system will increase. Means may be provided in associationwith the adapter lens housing 88 to allow a plurality of specificpositions relative to the indirect ophthalmoscopy lens 85 to be readilyobtained, such as stops or detents which will precisely position theadapter lens system, such as lens 86 accordingly. For example, theadapter lens may be moved to provide 5 diopter incremental changes insystem power or the like. This will allow net system power to beadjusted as desired for a particular clinical application. The otherexamples of adapter lenses shown herein may also be provided withhousings to allow selective and variable positioning of the adapter lenssystem relative to the indirect ophthalmoscopy system.

Turning to FIG. 5, an embodiment of the adapter lens system according tothe invention is shown in use with an indirect ophthalmoscopy lenssystem 90 which includes a contact lens 92 and an anterior image forminglens element 94. The indirect ophthalmoscopy lens system 90 may besimilar to that described in U.S. Pat. No. 5,046,836 issued to DonaldVolk, with various lenses as described by this patent being commerciallyavailable from Volk Optical, Inc. In use with such an indirectophthalmoscopy lens, the adapter lenses of the invention may again usedto vary the system power or imaging characteristics when combined withthe contact indirect ophthalmoscopy lens system 90. As an example of theindirect ophthalmoscopy lens 90, the contact lens 92 may include anaspherical concave surface 91 which closely matches the contour of thecornea of the eye, and an aspherical anterior convex surface 93 ifdesired. The anterior lens element 94 may also be a single or doubleaspheric bi-convex lens, which in combination with the contact lens 92,forms a high resolution, wide-field fundus image having predeterminedmagnification and imaging characteristics. In one example, themagnification of the indirect ophthalmoscopy lens system 90 is 1.0 witha predetermined field of view of approximately 80°. It may be desirableto increase the magnification of the indirect ophthalmoscopy lens system90 by addition of a negative power adapter lens, or alternatively toincrease the field of view of the system using a positive power adapterlens. Examples of adapter lenses include both plus and minus poweredlenses having from approximately -20 to +20 diopters. The adapter lens96 and its associated housing 98 are selectively attached to theindirect ophthalmoscopy lens housing 95 in a manner similar to thatpreviously described. The minus powered adapter lenses may be used toincrease the magnification of the indirect ophthalmoscopy lens system 90for diagnostic or laser treatment applications. As an example, anadapter lens having a nominal power of -14 diopters increases themagnification of the indirect ophthalmoscopy lens 90 to 1.4, in turnreducing the laser spot size an amount equal to the reciprocal of thelateral magnification of the lens for improved focal laser treatment inthe central retinal area. In a preferred embodiment, the adapter lens 96may be meniscus in shape with its concave surface 80 adjacent to theanterior surface of the contact indirect ophthalmoscopy glass imaginglens. The adapter lens concave surface 80 may be spherical with a radiusof 17 mm and the convex side 84 may be an oblate spheroid with an apicalradius of 31.2 mm and a (negative) eccentricity of 0.9. The diameter maybe 26 mm, with a center thickness 1.25 mm, utilizing a glass with anindex of retraction of 1.523. Although the addition of the adapter lens96 to the indirect ophthalmoscopy lens system will result in a change ofthe focal length of the lens system and therefore also a change of itsfocus relative to the entrance pupil of a patient's eye, the benefitsobtained by the addition of the adapter lens system outweigh a slightreduction in field size which may occur as a result of increased focallength. Alternatively, a positive power adapter lens 96 will increasethe power of the optical system, decrease the fundus imagemagnification, increase field of view and further allow the slit lampillumination to be angled further off-axis, so as to reduce reflectionsin the optical system.

The adapter lens systems of the present invention may also be usefulwith other types of ophthalmoscopic optical devices, such as directophthalmoscopy lenses or gonioscopy lenses, and the like. In FIG. 6, aknown Goldmann type three-mirror lens 100 is shown, which performsseveral useful diagnostic functions. In such a lens, a series ofreflecting surfaces 102, 104, and 106 are provided within a contact lens108. The contact lens 108 has a contact surface 110 and an anteriorplanar surface 112. Surfaces 102, 104, and 106 are inclined at varyingangles to the anterior surface 112. The semi-circular mirror 102 is usedfor gonioscopy, while rectangular mirrors 104 and 106 are used forexamination of the retrociliary region as well as peripheral regions ofthe retina. The posterior pole may also be observable through the axisof the contact lens 108. In use with such a lens, an adapter lens system114 of the invention may vary the magnification, field size, or imagingcharacteristics of the lens in a variety of manners. For gonioscopy, alower magnification may be preferred for studying the contours of theanterior chamber angle, wherein a minus power lens (not shown) may beeffectively used for such a purpose. Alternatively, to better view thetrabecular meshwork of the anterior chamber angle, higher magnificationmay be desirable, provided by means of a plus power adapter lens 116 orseries of small adapter lenses 120, 121, and 122 as shown in FIG. 6a,each of which are disposed in a housing 118. In FIG. 6a, the smalladapter lenses 120-122 are provided for each of the mirrors 102, 104,and 106 respectively, as well as for the central fundus view. Theadapter lenses 120-122 allow observation of the images from each of themirrors through central portion of each lens 120-122. Surfaces of suchan adapter lens may appropriately be plano, concave, or convex and maybe aspherical in contour to enhance imaging properties. Thus the virtualimage produced by such gonioscopy and direct ophthalmoscopy lenses maybe magnified without distortion.

In FIG. 7, a set of adapter lens systems according to the invention areshown, with the set generally designated 130 comprising at least twoadapter lens systems, each having at least one adapter lens element. Inthe adapter lens set 130, the adapter lens systems may include positiveand negative power lens systems, and may also include contact andnon-contact lens systems. More particularly, as shown in FIG. 7, the set130 may include a plus powered adapter lens system 132 having a pluspowered lens element 134 positioned within an adapter lens housing 136.The adapter lens housing 136 includes means, such as engaging tabs 138,associated therewith for selectively attaching the adapter lens housing134 to a housing associated with an ophthalmic lens system (not shown),such as the ophthalmic lenses shown in previous figures. The set 130 mayalso include another plus powered adapter lens 140 which may have adifferent nominal power than the adapter lens system 132. The set 130may further include a minus power adapter lens system 145 having apredetermined minus power, and/or additional minus power adapter lenssystems, such as lens system 150 which may have different nominalrefractive powers. The set 130 may further include a contact lensadapter system 155, and additional contact lens systems such as acontact adapter lens 160, which may have different nominal refractivepowers, and being plus and/or minus powered adapter lenses. Thedifferent adapter lenses act to modify the optical characteristics, suchas the net power, magnification, or other characteristics of theophthalmic lens system with which they are used in a selective andpredetermined manner. The set 130 may further include one or more filterlenses 165 to also modify the optical characteristics of the ophthalmiclens system. It should be recognized that the set of adapter lenses 130may vary to include plus or minus powered lenses, contact or non-contactlenses, each of which is designed to modify the optical characteristicsof the ophthalmic lens system in a selective and predetermined manner.

As should be recognized from the foregoing, the adapter lenses of theinvention may be used for modifying power and magnification of anophthalmoscopic or gonioscopic lens system, or alternatively used tomodify the imaging characteristics thereof. The adapter lenses may bedesigned to correct for imaging aberrations of the combinedophthalmoscopic lens system, and may use simple spherical or asphericalplano- convex, plano-concave, bi-convex, or bi-concave designsselectively positioned either in front of or behind the ophthalmoscopiclens system with which they are used. A wide variety of different poweradapter lenses may be used in association with a particularophthalmoscopic lens system to achieve various magnifications and systemcharacteristics. The adapter lens systems may include one or moreoptical elements and may be of the non-contact or contact type.Additionally, various of the preferred embodiments as described hereinmay be combined and used in conjunction with one another and anophthalmoscopic lens system to expand the application and use of theophthalmoscopic lens system. Although preferred embodiments of theinvention have been described, it is to be understood that variousmodifications would be obvious to those skilled in the art, and areembodied within the present invention as defined by the appendantclaims.

What is claimed is:
 1. An adapter lens system for use with an ophthalmiclens system in the examination or treatment of a patient's eyecomprising,at least one adapter lens element including first and secondsurfaces, said at least one adapter lens element being positioned withinan adapter housing, said adapter housing being selectively attached to ahousing associated with said ophthalmic lens system, said at least oneadapter lens element being positioned in predetermined relation to alens of said ophthalmic lens system, wherein said at least one adapterlens modifies the optical characteristics of said ophthalmic lens systemin a selective and predetermined manner, wherein said ophthalmic lenssystem includes at least one mirror to view different portions of thefundus or anterior chamber angle, and said adapter lens system includesat least one lens element for said at least one mirror.
 2. The adapterlens system of claim 1, wherein,said at least one adapter lens elementis a non-contact lens.
 3. The indirect ophthalmoscopy lens system asrecited in claim 2, wherein,at least one of said two lenses includes atleast one surface being an aspheric surface of revolution.
 4. Theindirect ophthalmoscopy lens of claim 2, wherein,said at least one lensis moveable to modify the net power of the combination of said at leasttwo lenses forming the indirect ophthalmoscopy lens system.
 5. Theindirect ophthalmoscopy lens of claim 2, further comprising,a contactlens positioned in space relationship to said at least two lenses, saidcontact lens including a posterior surface for placement upon the corneaof said patient's eye.
 6. The adapter lens system of claim 5, 1wherein,said at least one adapter lens element is a contact lens.
 7. Theadapter lens system of claim 1, wherein,said means for selectivelyattaching said adapter housing includes an outer surface on said adapterlens housing which is frictionally engagable on an interior surface ofsaid housing of said ophthalmic lens system.
 8. The adapter lens systemof claim 7, wherein,said outer surface includes resilient meansassociated therewith for frictionally engaging said interior surface ofsaid ophthalmic lens housing.
 9. The adapter lens system of claim 8,wherein,said resilient means is an o-ring positioned on said outersurface which frictionally engages said interior surface and provides aseal between said adapter lens housing and said ophthalmic lens systemhousing.
 10. The adapter lens system of claim 1, wherein,said at leastone adapter lens element has at least one aspherical surface with itsmagnitude and shape defined by the polynomial expressed as follows:

    y=(2rx+(e.sup.2 -1)x.sup.2).sup.1/2 +Ax.sup.F +Bx.sup.G +Cx.sup.H ;

where r equals the apical radius of curvature of the surface, e equalsapical eccentricity of the surface, and the co-efficients A, B, and Cequal successive terms in the polynomial, and F, G, and H equalexponents in the successive terms respectively, wherein at least theapical radius of curvature and apical eccentricity of said at least oneaspheric surface are chosen to satisfy optical correction of imageaberrations including curvature, astigmatism, and distortion.
 11. Theadapter lens system of claim 1, wherein,said at least one adapter lenselement is selectively movable along the optical axis of said ophthalmiclens system to modify the net power of the resulting optical system. 12.The adapter lens system of claim 1, wherein,said ophthalmic lens systemis a gonioscopy lens system.
 13. An indirect ophthalmoscopy lens for usein the examination or treatment of a patient's eye, comprising,at leasttwo lens elements, each having first and second co-axial surfaces withat least one of said lens elements including an aspheric surface ofrevolution with its magnitude and shape defined by the polynomialexpressed as follows:

    y=(2rx+(e.sup.2 -1)x.sup.2).sup.1/2 +Ax.sup.F +Bx.sup.G +Cx.sup.H,

where r equals the apical radius of curvature of the surface, e equalsapical eccentricity of the surface, and the co-efficients A, B, and Cequal successive terms in the polynomial, while F, G, and H equalexponents in the successive terms respectively, said at least two lenselements positioned adjacent one another such that the refractiveproperties of each are combined, said at least two lens elements beingpositioned in spaced apart relationship to to the patient's eye, said atleast two elements collecting light rays emerging from points frompoints on the fundus of the patient's eye and refracting said emerginglight rays to form a real image of the fundus, wherein each of said atleast two hens elements includes posterior and anterior surfacesrelative to said patient's eye, with a first lens positioned nearest tosaid patient's eye and a second lens positioned further from saidpatients eye, wherein the anterior surface of said first ledge and theposterior surface of said second lens are convex surfaces, and whereinsaid posterior surface of said first lens and the anterior surface ofsaid second lens consist of a surface selected from the group ofsurfaces comprising a convex spherical surface, a convex asphericalsurface, a plano surface and a concave surface.
 14. The indirectophthalmoscopy lens of claim 13, wherein,each of said at least two lenselements are biconvex lenses, with adjacent surfaces of each of saidlens elements having a curvature which is more highly curved than theother surface of each said at least two lenses.
 15. An indirectophthalmoscopy lens for use in the examination or treatment of apatient's eye comprising,at least two lens elements each having firstand second co-axial surfaces with at least one of said lens elementsincluding an aspheric surface of revolution with its magnitude and shapedefined by the polynomial expressed as follow:

    y=(2rx+(e.sup.2 -1)x.sup.2).sup.1/2 +A.sup.F Bx.sup.G Cx.sup.H ;

where r equals the apical radius of curvature of the surface e equalsapical eccentricity of the surface, and the co-efficients A, B, and Cequal successive terms in the polynomial, while F, G, and H equalexponents in the successive terms respectively, said at least two lenselements positioned adjacent one another such that the refractiveproperties of each are combined, sale at least two lens elements beingpositioned in spaced apart relationship to the patient's eye, said atleast two lens elements collecting light rays emerging from points onthe fundus of the patient's eye and refracting said emerging light raysto form a real image of the fundus, wherein, at least one of said atleast two lens elements is moveable relative to other of said lenses,with the position of said at least one lens being selectively variableto modify the optical characteristics of the combination of said atleast two lenses, and wherein each of said at least two lenses includeposterior and anterior surfaces respectiveIy in relation to thepatient's eye, wherein each of said posterior and anterior surfacesconsist of a surface selected from the group of surfaces comprising aconvex spherical surface, a convex aspherical surface, a plane surfaceand a concave surface.
 16. The indirect ophthalmoscopy lens of claim 15,wherein,said at least one aspherical surface has continuous andprogressive change in curvature peripheralward and is non-spherical overits extent.
 17. The indirect ophthalmoscopy lens of claim 15,wherein,each of said at least two lens elements are biconvex lenses,with adjacent surfaces of each of said lens elements having a curvaturewhich is more highly curved than the other surface of each said at leasttwo lenses.
 18. The indirect ophthalmoscopy lens of claim 15,wherein,said optical characteristics of the combination of said at leasttwo lenses comprise image magnification.
 19. An indirect ophthalmoscopylens system comprising,at least two lenses positioned in spaced apartrelationship along an optical axis such that the optical properties ofsaid at least two lenses combine to form a real image of the fundus of apatient's eye, wherein at least one of said at least two lenses ismoveable relative to the other of said lenses, with the position of saidat least one lens being selectively variable to modify the opticalcharacteristics of the combination of said at least two lenses, whereinone of said at least two lenses is a plus powered lens and the other isa negative powered lens, wherein said negative powered lens providesincreased image magnification when moved relatively toward or positionedimmediately adjacent to said plus powered lens.